Implement bin/repository thaw for unfreezing cluster repositories
Ref T10751. Add support tooling for manually prying your way out of trouble if disaster strikes.
Refine documentation, try to refer to devices as "devices" more consistently instead of sometimes calling them "nodes".
Test Plan: Promoted and demoted repository devices with bin/repository thaw.
Reviewed By: chad
Maniphest Tasks: T10751
Differential Revision: https://secure.phabricator.com/D15768